I have a switch (LSW6-GT-8NS) connected to my router. Switch is connecting to my PC. All cables PC⇨SWITCH⇨ROUTER⇨OUTSIDE are CAT6. All works fine (Tested). My PC is set to 1000Mbps Full Duplex (connection from switch to PC is green, showing full duplex) . Also my router is set to 1000Mbps Full Duplex. But connection from router to switch becomes orange color (100Mbps) after some time when IPv6 settings are switch off in the router's settings. The problem here is that my provider do not use IPv6 so the router when set to enable IPv6 is "connecting" forever and spamming errors to logs. The connection looks good (all green) though. What should I do? Can I let router spamming "ERROR 0days, 00:04:42, [rtadvd]send RA failed: 55" forever? 

Could disabling IPv6 in the pc's settings do the job? the PC is a Linux, so it is really easy to disable.